1. Field of the Invention
The present invention relates generally to back-lit buttons, and more particularly to a button assembly and method of making the same including an opaque formed cap of any simple or complex shape wherein the cap includes a graphic image formed therewith having a first color visible in daytime or direct light and one or more different colors when back-lit, and wherein further, the graphic image is not susceptible to wear or accumulation of residue during use and the assembly can direct light through the graphic image in a predetermined direction.
2. Description of the Related Art
Back-lit buttons are typically utilized on control panels and dashboards of automobiles and provide a graphic image on a substantially planar exterior face of the button which identifies the function of the button, such as a "door lock" button or the like. These buttons are usually formed from plastic and are provided with a dark major opaque color, such as black, and a clear window therethrough having a graphic image thereon of a contrasting color, such as white or gray, which is translucent and referred to as a "daytime color." When the graphic is back-lit with a light source of a different "nighttime color," such as green, blue, red or orange, the nighttime color radiates through the daytime color and the graphic image is seen by a user having the nighttime color.
An example of such a back-lit button is provided by what is known in the art as the "Paint and Laser Method" an example of which is illustrated in FIG. 18. As described in detail below, this method typically includes applying a white translucent layer of material, which provides the daytime color, over a color tinted translucent plastic button, which provides the nighttime color. An opaque black layer of material is then applied over the white layer and a laser is directed against the black layer so as to etch a desired graphic image through the black layer only, exposing the white layer underneath. Thus, the graphic image is provided in white for daytime viewing and, when the tinted plastic button is back-lit from an external light source, the color of the tinted plastic can be seen through the white translucent layer for nighttime viewing.
The graphic images on these buttons, however, are on the front exterior or "first surface" of the button which faces outward from the control panel and is repeatedly contacted by a user. Thus, they are readily susceptible to wear and image erosion as well as residue accumulation over and within the recesses forming the image which serve to render the image unreadable. Additionally, since the tinted plastic button provides the nighttime color, it is difficult to provide more than one nighttime color per button.
Back-lit buttons also are known which have a graphic image formed on an interior or "second surface" of the button and are provided by what is known as a "Formed Cap Process." An example of such a process is disclosed, for example, in U.S. Pat. No. 5,098,633 which is owned by the same assignee as the assignee herein.
In that patent, silk screening techniques are utilized to provide an opaque black layer having a clear graphic image area upon one side of a transparent flat sheet. A white or gray daytime color layer and one or more nighttime color layers are then applied over the clear graphic image area. Thereafter, the sheet is thermoformed into a cap of a desired shape and filled with transparent resin on the side of the sheet containing the graphic image and color layers. Alternatively, the cap is applied over and adhered with resin to a pre-formed transparent support structure so as provide a finished button. Thus, the graphic image, color layers and resin are on the "second surface" of the cap and the opposite "first surface" or exterior of the cap is contacted by a user so that the image is not susceptible to wear or residue accumulation.
Although this process is successful when the sheet is thermoformed into a cap having a relatively flat or slightly curved surface upon which the graphic image is provided, the graphic image can become distorted when the sheet is thermoformed into a cap having a graphic image display surface which is of a complex three-dimensional shape. In such a situation, it is difficult to control the distortion or stretching of the sheet during thermoforming. Although the distortion can be somewhat predicted and accounted for before thermoforming, it is difficult to precisely determine the distortion and provide the quality and consistency necessary for mass-production of such buttons.
Additionally, in automobiles, illumination from dashboard displays and back-lit buttons at night causes glare to be reflected off the windshield into the driver's eyes. This glare is typically reduced or eliminated by extending a ledge from the dashboard above the displays so as to block the light from reflecting off the windshield.
Another method is to utilize what is known in the art as a "light control film" or "LCF", illustrated in FIGS. 16-18, which directs the light emitted from a display or back-lit button in a desired direction away from the windshield. As described in detail below, the LCF includes a core formed by a plurality of alternating opaque louvers and transparent layers which are sandwiched between two layers of thin clear film. LCFs, however, are applied to the exterior "first surface" of the display or button on top of the graphic image which detracts from the daytime image of the graphic image and, due to the very thin layer of film over the louvers, the film can be readily scratched thereby distorting the effects of the LCF and exposing the core to scratching or wear. Additionally, for the LCF to work, the surface over which the LCF is applied must be substantially planar.
Accordingly, it is desirable to provide a button assembly and method of making the same including an opaque formed cap of any simple or complex shape wherein the cap includes a graphic image formed therewith having a first color visible in daytime or direct light and one or more different colors when back-lit, and wherein further, the graphic image is not susceptible to wear or accumulation of residue during use and the assembly can direct light through the graphic image in a predetermined direction.